1. Field of the Invention
The present invention consists of a high-capacity centrifugal pump. Such a pump may be used to transport a wide variety of liquids, to fulfill a broad range of applications wherever a pump of this type may be required.
2. Description of the Prior Art
Centrifugal pumps (sometimes referred to by the pump industry as "the king of pumps") were invented in France around the middle of the nineteenth century. Before their introduction to the pumping industry, only positive displacement pumps were available (i.e., specifically, piston and rotary types). These were costly to manufacture since the machine tool industry had not been well developed and high-production techniques were generally unknown. Centrifugal pumps, because of their inherent simplicity, durability and low fabrication cost, quickly replaced more expensive positive displacement pumps and the bulk of pump research and development throughout the world was slanted to the perfection of the many varieties of velocity (centrifugal) pumps required by growing industries. Today, the most widely used pump type is of the centrifugal variety since it combines many of the most desirable attributes required of pumps in general use. A major improvement in centrifugal pump design and performance should be of significant value to the pumping industry and especially to the end user who pays for everything.
Small (less than 500 GPM capacity) centrifugal pumps are notoriously inefficient, due, principally, to the low velocity imparted to the fluids pumped when such pumps are driven by commonly available drive means such as 1725 RPM or 3450 RPM electric motors. In addition, small centrifugal pumps have a low ratio betwen contained volume and their interior surface resulting in a relatively high level of friction between the moving fluid and the impeller and pump chamber walls. Large centrifugal pumps with impellers of greater diameter and width impart high velocity to the fluids they transport and a higher ratio between contained volume and interior surface is present thereby reducing friction and improving efficiency. Comparatively few small centrifugal pumps develop hydraulic horsepower efficiencies in excess of 50% at maximum head in contrast to very large pumps capable of efficiencies of 91% and slightly higher. It is further true that the useful life of larger pumps is generally greater than that of smaller pumps since the larger pumps may be operated effectively at lower speeds, reducing wear on moving parts.
Contrary to the commonly-held belief by centrifugal pump designers and engineers, it has been discovered that fluids to be pumped need not dwell in the compartments of centrifugal pump impellers for the length of time long considered essential to impart maximum velocity to the fluids pumped. The scientific principle that a moving body's kinetic energy does not change unless there is a change in its velocity may be applied to advantage in centrifugal pump design and operation. This discovery has been applied to the subject invention described below and its application combined with improved basic impeller and pump chamber design has resulted in a centrifugal pump which exhibits several desirable characteristics setting it apart from other centrifugal pumps currently known to the prior art. The present invention differs from the prior art in several respects relative to operational efficiency, energy input requirements, manufacturing costs and overall versatility owing to the following reasons.
In the past, numerous attempts have been made to improve the poor efficiency of small and medium-size centrifugal pumps, these efforts devoted mainly to changes in impeller design and casing configurations. It appears the bulk of such activities have been based upon well-established "scientific" rules which have caused many researchers to by-pass the fundamental principles which form an integral part of the performance of such devices. It has been widely believed significant hydraulic efficiency could only be attained by physically large centrifugal pumps, that small pumps could not compete successfully because of their small size. It has been believed that pump impellers must be relatively narrow in width, that increasing the dimensions of impellers in that plane would serve no useful purpose. A further belief held that significant liquid velocity could only be obtained by causing the liquid to be pumped to travel a comparatively long path between impeller blades, to "give it time to accelerate". The several experimental prototypes which have formed the basis for the present invention have pointed out the shortcomings of many of the earlier efforts to produce high-efficiency small centrifugal pumps. It has been proven by actual tests of the experimental pumps which led to the present invention that impeller diameter and speed of impeller rotation are more significant to the imparting of kinetic energy to a liquid pumped than impeller blade length, that increasing impeller capacity by increasing its width both increases capacity and reduces frictional drag upon the liquid pumped, both major elements contributing to efficiency.
The subject invention differs from the prior art in that, in spite of its comparatively small size, it performs much like a physically larger pump, i.e., its internal dimensions are such that the liquid volume it transports is high in relation to the surface of the pump's impeller and chamber walls, thereby reducing internal friction. For example, the invention's impeller width is almost as great as its diameter. This "abnormally" wide impeller thereby requires a wide pump chamber in which to revolve, the result in effect simulates some of the internal dimensions of much larger pumps. Since the capacity of the pump is maximized by the design of its impeller, operation closely approaches that of much larger pumps and the pump's efficiency is thereby increased.
Energy input requirements relative to volume pumped are reduced because of the pump's efficiency. For example, a standard, well-designed centrifugal pump having the same external dimensions of the subject invention would be capable of transferring from 70 to 100 gallons of water (per minute) to a head of 5 feet driven by a 1 HP motor at 3450 RPM. The subject invention is capable of transferring 165 gallons of water per minute to a head of 5 feet operating under identical conditions, an increase in hydraulic horsepower efficiency from 65% to 135%. Actual hydraulic horsepower efficiency of a centrifugal pump moving water to a 5-foot head and absorbing 1 HP would range from 9% for 70 GPM to 13% for 100 GPM, where as the efficiency of the subject invention is 21%, an increase of from 65% to 135%. The comparison made is for low-head delivery. Hydraulic horsepower efficiencies for most centrifugal pumps generally increase at higher heads reaching a limit of efficiency close to maximum head capacity. The subject invention performs in a similar manner and maintains its volume and efficiency advantage over conventional centrifugal pumps over its entire performance range.
Manufacturing costs of the subject invention are significantly lower than those of prior-art pumps of equivalent capacity since the invention is physically much smaller, thereby less material is required and fabrication and assembly charges are reduced. The current production model, constructed principally of 6061 aluminum alloy, is of massive construction but weighs only 5 Lbs. which weight includes mounting legs and inlet and outlet nozzles for the use of hoses. A close-coupled version of the invention to be mounted directly on the end of an electric motor would weigh only 4 Lbs. The current model's impeller weighs only 4 oz.
The subject invention is distinctly versatile in that it can transfer a wide range of liquids, either clear or containing semi-solid or even solid particles small enough to pass between the pump's impeller vanes. In addition, because of the pump's small size and light weight, it can be easily installed where pumps of equivalent capacity and of greater external dimensions cannot be utilized because of space limitations. The cost of shipping the subject invention is materially reduced because of its light weight and small size as compared to other centrifugal pumps of the same capacity. Field repair is greatly facilitated due to the pump's small size and light-weight components as compared to other centrifugal pumps of the same capacity and performance. The subject invention, because of its high efficiency, uses only 50% of the energy required by conventional centrifugal pumps of equivalent capacity. Thus the motors used may be smaller, lighter, and of lower cost, this in addition to significant savings in electrical energy.
Pressure developed by the subject invention is comparable to that of prior-art small centrifugal pumps utilizing impellers of the same diameter and rotated at the same speed. The invention's impeller is excessively wide as compared to conventional impeller design but tests have shown the impeller width, partially responsible for the high-volume-to-pump-weight ratio, has little to do with developed hydrostatic pressure. An impeller of the same basic design, but much narrower, was tested and developed the same pressure as the wider impeller, but the flow rate was greatly reduced.
One prototype incorporates an impeller of 2.5 In. diameter and develops a static (no flow) pressure of 16 psi. at approximaty 3450 RPM which permits the pump to operate effectively to a head of at least 32 feet. Another experimental model of similar design, utilizing an impeller of 3.5 In. diameter, developed a static pressure of 24 psi, at approximately 3450 RPM. It would appear that increasing the impeller diameter by a factor of 0.4 would result in an increase in pressure by a factor of 50% providing RPM and all other conditions remain constant. If such a conclusion proved valid by constructing and testing pumps designed in the manner taught by the subject invention's technology, then it could be expected to develop a pressure of 36 psi. from an impeller of 4.9 In, diameter, a pressure of 54 psi. from an impeller of 6.86 In. diameter, a pressure of 81 psi. from an impeller of 9.604 In. diameter, etc. The subject invention is designed to operate with conductors of 2.5 In. internal diameter, this in keeping with the purpose of the total operational design, i.e., reduction of friction losses to a minimum by keeping the cross section of liquid flow very large in relation to the area of the impeller, the pump chamber walls and the conductors, both inlet and outlet.
The current invention prototype, although very small, is capable of performance greatly superior to that of other centrifugal pumps of equal external dimensions and represents the basic design for centrifugal pumps of virtually any size and capacity. The tested and calibrated performance of the invention has proven the practicality of its design which lays the foundation for a wide range of centrifugal pumps of various sizes designed for a variety of applications. It is anticipated the development of the unique combination of design principles of the invention will result, it thoroughly explored, in a lasting contribution to all concerned with the advantages offered.